Oxidative metabolism of polyunsaturated fatty acids (PUFAs) gives rise to a group of oxygenated compounds, called oxylipins, which regulate essential physiological processes in multicellular organisms. Our long-term research objective is to understand the general principles governing the synthesis and metabolism of oxylipins, and to dissect the molecular mechanisms by which these bioactive substances regulate defense-related processes. In the present application, we will build on our previous success in establishing Lycopersicon esculentum (tomato) as a model system for molecular genetic analysis of systemic induced resistance to herbivorous arthropods. The proposed research seeks to test the hypothesis that the fatty acid-derived plant hormone jasmonic acid (JA) is an intercellular signal for host defense responses, and that the biosynthesis of JA is regulated by the peptide signal systemin. The specific aims of the project are: (i) to use a map-based approach to clone and characterize the Sprl gene that plays a role in systemin perception; (ii) to complete map-based cloning of the JL1 gene that is required for the metabolism or transport of 12-oxo-phytodienoic acid, a cyclopentenone precursor of JA; (iii) to use genetic chimeras to analyze the role of JA biosynthesis and JA perception in intercellular wound signaling; and (iv) to combine biochemical and functional assays to analyze phloem exudate for the presence of JA, systemin, and other signals that induce defense gene expression. The systemin/JA signaling pathway provides a unique opportunity to study the mechanism by which peptide and oxylipin signals coordinate systemic immunity. The biochemical pathways for oxidative metabolism of PUFAs in plants are remarkably similar to those involved in the production of arachidonic acid-derived compounds that play an essential role in numerous aspects of human health and disease. Thus, the proposed research is expected to illuminate general principles of oxylipin metabolism in diverse biological systems. Results obtained from these studies will also provide insight into specific mechanisms by which fatty acid-derived signals regulate host defense responses and, more generally, the role of PUFAs in healthy and diseased organisms.